It’s a standard sign at many convenience and grocery stores around the country, usually posted near the prepared food line and aimed at customers paying by Electronic Benefits Transfer, the debit card for food stamps.

But when an economics professor posted a photo of the sign at a Pennsylvania Wawa to Twitter, thousands reacted with astonishment.

“EBT Customers,” the sign reads. “According to EBT guidelines, any item or ingredient that is hot, toasted or on toasted bread or roll is not eligible for purchase with EBT.”

Wrote Matthew Incantalupo, the econ professor who snapped the photo: “Social policy in the United States: poor people don’t get hot food.”

This is, in fact, long-standing social policy in the U.S. — and some people want it to become even more restrictive.

Since the passage of the Food and Agriculture Act of 1977, people on food stamps have been banned from using their benefits to buy hot food, except in an extremely narrow set of circumstances. Last year, the Obama administration moved to crack down on establishments that sold SNAP users pizza slices and other food cold, and then offered to microwave it for them.

The logic, as explained by the Department of Agriculture, is that food stamps are intended to help provide food for home consumption, not food generally. USDA encourages SNAP recipients to buy staples, such as bread, cereal, fruit and vegetables, meat, fish and dairy, and maintains a recipe database to show recipients how to cook at home affordably.

There are some exceptions. In the case of a natural disaster or other emergency, USDA can temporarily approve hot food benefits for people without access to a kitchen. That exception was invoked in Louisiana during severe flooding last winter.

A handful of counties, including a number in California, also maintain a special project called the Restaurant Meals Program, which allows the elderly, disabled and homeless to use food stamps at approved restaurant locations.

However, national participation has shrunk steadily since the 1990s. When SNAP food restrictions come up in policy debates now, it’s typically in regards to making them stricter, not more lenient.

A number of public health groups, including the American Medical Association and the American Heart Association, have called on Congress to ban soda and other junk foods from SNAP.

The AMA recently called on Congress to “harmonize SNAP food offerings with those of the Special Supplemental Nutrition Program for Women, Infants, and Children,” or WIC — a program that only allows participants to buy from a limited list of healthy foods and ingredients.

But such restrictions are staunchly opposed by the grocery industry, which says it would have to completely overhaul its point-of-service software to prevent soda purchases with EBT. And many anti-hunger advocates and defenders of SNAP say such restrictions would further stigmatize the poor and deny them basic autonomy over what they eat.

Incidentally, those concerns are also out in force in the responses to Incantalupo’s tweet.

“A good number of people on SNAP work full time and don’t always have the time/energy to cook,” one man wrote. “... A hot meal should not be considered a luxury. Not in one of the wealthiest countries in the world.”